Is Tc99m-MIBI scintigraphy a predictor of response to pre-operative neoadjuvant chemotherapy in Osteosarcoma?

Abstract

<em>Objectives:</em> Multidrug resistance (MDR), which may be due to the over expression of P-glycoprotein (Pgp) and/or MRP, is a major problem in neoadjuvant chemotherapy of osteosarcoma. The aim of this study was to investigate the role of Tc-99m MIBI scan for predicting the response to pre-operative chemotherapy. <br/><em>Materials and Methods:</em> Twenty-five patients (12 males and 13 females, aged between 8 and 52y) with osteosarcoma were studied. Before the chemotherapy, planar ^99mTc-MIBI anterior and posterior images were obtained 10-min [tumor-to-background ratio: (T₁/B₁)_10min] and 3-hr after tracer injection. After completion of chemotherapy, again ^99mTc-MIBI scan was performed at 10-min after tracer injection. In addition to calculation of decay corrected tumor to background (T/B) ratios , using the 10-min and 3-hr images of the pre-chemotherapy scintigraphy , percent wash-out rate (<em>WR</em>%) of ^99mTc-MIBI was calculated. Using the 10-min images of the pre- and post-chemotherapy scans, the percent reduction in uptake at the tumor site after treatment (<em>Red%)</em> was also calculated. Then after surgical resection, tumor response was assessed by percentage of necrosis. <br/><em>R</em><em>esults:</em> All patients showed significant ^99mTc-MIBI uptake in early images. Only 9 patients showed good response to chemotherapy (necrosis≥90%) while 16 patients were considered as non-responder (necrosis<90%). There was no statistical significant difference between non-responders and responders in (T₁/B₁)_10min.There was a significant negative correlation between <em>WR% </em>and percentage of necrosis (<em>P</em>=0.001). On the other hand, there was a significant correlation between <em>Red%</em> and percentage of necrosis (<em>P</em><0.001).There was also statistical significant difference in <em>WR%</em> and <em>Red%</em> between non-responders and responders (both P< 0.001). <br/><em>Conclusion:</em> Washout rate of ^99mTc-MIBI in pre-chemotherapy scintigraphy as well as Red<em>% </em>using pre- and post-chemotherapy MIBI scintigraphy are useful methods for predicting response to neoadjuvant chemotherapy.